405 FACT: Flute Activated Carbon Technique Datasheet

405 FACT Flute Activated Carbon Technique Datasheet PDF

solinst flute activated carbon technique

FACT – Flute Activated Carbon Technique

Model 405

FACT is an innovative method developed for mapping the dissolved phase contaminant distribution in a sealed borehole, with 6 inch to 3 feet (15 cm to 1 m) resolution.

A common practice is to combine the FACT with the NAPL Flute cover to locate both the non-aqueous and the dissolved phase. The NAPL Flute system is a reactive cover for the Solinst Flute Blank Liner.

The Solinst Flute Blank Liner is a fully removable solution designed to seal open boreholes to prevent cross-contamination.

For more information on Solinst Flute Blank Liners and the NAPL Flute and their installation, see the Model 405 Blank Liner and NAPL Flute Data Sheets.

FACT Construction, with the FACT stitched between the NAPL Flute cover (striped) and a diffusion barrier (silver)

figure 2 fact results for tce on a 6 inch scale

FACT resutls for TCE on a 6 inch scale

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How the Flute Activated Carbon Technique Works

The Flute Activated Carbon Technique involves the use of a 1.5″ (3.8 cm) continuous strip of activated carbon felt that is added to the NAPL Flute. The activated carbon felt is emplaced against the borehole wall during the eversion of a Blank Liner, or installation through direct push rods for overburden applications.

Once positioned against the borehole wall, the activated carbon felt wicks away the contaminants in pore spaces and fracture flows by diffusion. As the diffusion process takes place in a sealed borehole, the concentrations recorded during the technique are not influenced by cross contamination and/or leakage issues. The pressure exerted by the Blank Liner on the borehole wall (generally 5 to 10 feet (1.5 m to 3 m) of water pressure) creates a strong seal which prevents preferential flows from developing.

Concerns of influence by contact with borehole water are put to rest by the protection provided by the hydrophobic NAPL Flute cover and speedy installation and removal procedures, which minimize interval exposure times to a few seconds. As a precaution, the borehole water is usually pumped from the hole as the Blank Liner is everted.

After two weeks, the FACT installation is removed from the well, cut into the desired sample intervals (6 inches to 3 feet (15 cm to 1 m)) and sent to the lab for analysis (EPA 8265).

FACT Installation

Installation Times

Solinst Flute Blank Liner systems should be installed as quickly as possible after the hole is drilled to minimize cross connection effects of the borehole water on the pore water in the open borehole.

Reaction Times

Vadose Zone
The FACT is typically left in place for 48 hours for a vadose zone installation to allow the diffusion process from the formation into the carbon.

Saturated Zone
The FACT should be left in place in the saturated zone for about two weeks due to the diffusion coefficient being much smaller in water than in air. A diffusion calculation shows that two days is long enough to “see” about 0.5 cm into the borehole wall with 7% porosity. Concentration in pores is 2,700 ug/L. That improves after two weeks.

diffusion of tec at indicated days along axis in plane geometry with 7% porosity and and a carbon sink at 15.15 cm

Academic Analysis of the FACT

A master’s thesis is available by Monique Beyer of the Danish Technical University which is a rigorous assessment of the FACT analysis method and its use for a fractured rock site.

FACT Method Results

The measurements obtained by the FACT method representative and, therefore, show where the true contaminant peaks are located at depth. The replica contaminant distribution and Solinst Flute Transmissivity Profiling data (see the Model 405 Transmissivity Profiling Data Sheet) can be used to design a multilevel groundwater sampling system, such as the Water Flute (see the Model 405 Water Flute Data Sheet) and fate/ transport conceptual site models.

fact flute activated carbon technique results

Transmissivity Profile and FACT data. Note the high TCE concentrations at 112 feet and 140 feet BGS (Below Ground Surface) in very low transmissive fractures compared to low TCE concentrations in high flowing fractures at 90 feet and 130 feet. The TCE concentrations at 140 feet and 112 feet are the same or twice as high, respectively, as the highest flowing fracture in the borehole at 130 feet despite the fact that they are two of the lowest flowing fractures in the borehole. This data emphasizes the need for high resolution methods rather than coarse measurements to assure that all significant contaminant source zones are properly identified during characterization. Water Samples (green diamonds), validate the FACT concentrations.

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